The Role of .NET Namespaces
The FCL organizes its huge set of services using a concept called namespaces.   A namespace is a logical,
hierarchical organization of types similar to Java packages.  All .NET types “live” in a namespace. To use a
type, you must refer to it using its fully qualified name (i.e., including the namespace).  The FCL defines a large
number of namespaces that contain a ton of services usable from all .NET languages.

You can access a type defined within a namespace in a couple different ways.  You can use the fully qualified
type name, e.g., namespace.typename.   

For example, the Console class lives in the System namespace:

    Class TesterMain
       Shared Sub Main()
          'Namespace.TypeName.Method
          System.Console.WriteLine("Hello world")   
       End Sub
    End Class

Since typing namespaces is tedious, most .NET languages provide a shortcut mechanism.

VB has an 'Imports' keyword:
    Imports System
    Imports System.Drawing
    Imports System.Collections

C# has a 'using' keyword (note the case and semicolon):
    using System;
    using System.Drawing;
    using System.Collections;

Here is an example:
    Imports System
    Imports System.Collections

    Namespace Test
      Class TesterMain   
        Shared Sub Main()    
          'Use the System.Console class
          Console.WriteLine("Hello world")

          'Use the System.Collections.ArrayList class.
          Dim myList As ArrayList
          myList = New ArrayList()   
        End Sub      
      End Class
    End Namespace

Here is a partial list of some of the core .NET namespaces.

    System
    Contains numerous types dealing with primitive data, mathematical manipulations, garbage collection,
    and whatnot.

    System.Collections
    System.Collections.Generics
    Defines a number of container types.

    System.Data
    System.Data.OracleClient
    System.Data.SqlClient
    Contains types for database interaction.

    System.Drawing
    System.Drawing.Printing
    Contains numerous classes wrapping GDI+ primitives such as bitmaps, fonts, icons, printing support,
    and advanced rendering classes.

    System.IO        Contains types for streaming IO to a variety of devices, including files.

    System.Reflection
    Contains types that provide runtime type discovery.

    System.Runtime.InteropServices        Provides facilities to interact with unmanaged code (e.g., Win32
    DLLs and COM servers).

    System.Security        Contains types dealing with permissions, cryptography, and so on.

    System.Threading        Provides types for spawning and controlling threads.

    System.Web        Contain numerous types specifically geared towards the development of web
    applications, including ASP.NET.

    System.Windows.Forms        Provides types that facilitate the construction of more traditional Win32
    windows, dialog boxes, and custom widgets.
     
Your real challenge as a .NET developer is to learn about the wealth of types that ship with the .NET base class
libraries.     MSDN (your local help system, which is also available online) has a specific book that describes
each and every namespace (and all the contained types.  Look up the ".NET Framework Class Library" book
for full details.
Copyright (c) 2008.  Intertech, Inc. All Rights Reserved.  This information is to be used exclusively as an
online learning aid.  Any attempts to copy, reproduce, or use for training is strictly prohibited.
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